Geology & Geophysics Feature

A Meeting That Helped Foster the Acceptance of Global Tectonics

Fifty years ago, in the United States added their heft to a theory with profound implications: Earth's ocean crust recycles itself on a global scale, and continents move across the face of the planet.

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This week, scientists from across the world are gathered at the American Geophysical Union’s (AGU) Fall Meeting in San Francisco, Calif. They attended to be a part of history—at such meetings, those who convene present new results, build collaborations, refine ideas, and engage in discussions that could change the very course of our science.

Iceland’s Thingvellir rift, a site of spreading phenomena first discussed at the History of the Earth's Crust Symposium.
The central rift of the Reykjanes Ridge passes across Iceland as seen in this section found in Thingvellir National Park. At this rift, one can see evidence of seafloor spreading. Credit: Chris Ford, CC BY-NC 2.0

For those involved with seismology, paleomagnetism, and global tectonics, this year’s event marked an important anniversary of another meeting 50 years ago. On 11–12 November 1966, a crucial private meeting took place in New York at the NASA Goddard Institute for Space Studies. Called the History of the Earth’s Crust Symposium, the gathering brought together geologists and geophysicists interested in the evolution of continents and oceans, especially in new ideas pertaining to continental drift and the origins and history of the ocean floors.
At the time of the meeting, geologists, who generally fell into two theoretical camps—the fixists and the mobilists—had been pondering a variety of hypotheses that explained the features on Earth’s surface. Since World War II, additional observational data had come to light that offered clues to the physical mechanisms underlying those features. Might it be possible that the continents were moving across the face of the planet, and could the emerging field of paleomagnetics explain past movement?

An Auspicious Time

The History of the Earth’s Crust Symposium occurred at an auspicious time in the geological sciences. While the idea of continental drift was not new, evidence pointing to the mechanism of drifting was under much debate. New evidence bearing on the evolution of Earth’s crust was just coming to light, from magnetic analysis of surface rocks, sediment cores, and shipboard magnetics data and from seismic data from the world’s oceans. Much of this new information was still unpublished at the time of the meeting.

John Dewey of Cambridge discusses the Appalachian-Caledonian mountains at the History of the Earth’s Crust Symposium.
John Dewey of Cambridge University discusses the origins of the Appalachian-Caledonian mountain range at the History of the Earth’s Crust Symposium. Credit: Barrett Gallagher

The meeting was organized by geochemist Paul Gast of the Department of Geology at Columbia University and astronomer Robert Jastrow, director of the Goddard Institute. These organizers realized that new research on geomagnetic reversals, earthquake activity, the nature of the oceanic crust, and the causes of tectonic episodes was coming together in ways that presaged a revolution in the study of Earth’s evolution.

The guest list was impressive and included Harry Hess and Fred Vine of Princeton; Maurice Ewing, Lynn Sykes, James Heirtzler, Xavier Le Pichon, Neil Opdyke, and Walter Pitman from the nearby Lamont Geological Observatory; Henry Menard of the University of California, San Diego; Edward Bullard, John Dewey, and Dan McKenzie from Cambridge University; Patrick Hurley of the Massachusetts Institute of Technology; Marshall Kay of Columbia; and other geological luminaries.

It marked the first time that geologists and geophysicists came together to focus on what became the new global tectonics [Phinney, 1968]. This is significant because many of the last holdouts against the idea of continental drift—spurred by what they felt was a lack of scientific evidence—were from the United States [Oreskes, 1999]. But this meeting provided intellectual and disciplinary credibility that helped nudge the community to accept the basic ideas behind continental drift.

A Focus on Geomagnetic Reversals

The attendees were particularly interested in new results related to Earth’s magnetism and the subject of geomagnetic reversals. Meeting attendees knew that Earth experienced episodes when the geomagnetic poles flipped, when geomagnetic north became south and south became north.

Marshall Kay of Columbia discusses the Appalachian-Caledonian orogeny at the History of the Earth’s Crust Symposium.
Marshall Kay of Columbia University points out the positions of the continents during the Appalachian-Caledonian orogeny, an event that occurred prior to the opening of the present Atlantic Ocean. Kay’s talk was one of several at the History of the Earth’s Crust Symposium. Credit: Barrett Gallagher

Prior to the meeting, Allan Cox of Stanford and Richard Doell and Brent Dalrymple of the U.S. Geological Survey in Menlo Park, Calif., had established the timescale of reversals of Earth’s magnetic field for the past few million years [Cox et al., 1964]. They had accomplished this by measuring the magnetic polarities and ages of volcanic rocks from many different oceanic islands and some continental areas.

Their methods will be familiar to anyone who’s worked on paleomagnetism since then: They carefully drilled oriented samples from volcanic lava flows and measured their direction of magnetization in the lab. At the same time, they performed radiometric dating of their samples to provide a time history for the magnetic flips they detected. They found that during specific time intervals, paleomagnetic signatures followed the same pattern worldwide.

The internal consistency of the worldwide paleomagnetic and radiometric results established that the polarity events were the result of a rapid switching of the geomagnetic poles and could be correlated from one place to another. Cox, Doell, and Dalrymple brought this new insight to the History of the Earth’s Crust Symposium.

Signatures in Ocean Sediment

At the same time, Neil Opdyke and his students at the Lamont Geological Observatory were studying sediment cores from the ocean floor. These sediments, the researchers found, contain grains of magnetite that align themselves in the direction of the magnetic field at the time they were deposited. In this way, the scientists were able to determine the direction of the Earth’s magnetic field as a function of time downward through the cores [Opdyke et al., 1966].

Opdyke’s team presented these new results at the symposium. Together, the researchers verified a remarkable result: Ocean sediment cores vertically showed in detail the same sequence of reversals found in the volcanic rocks dated by Cox, Doell, and Dalrymple. The field of magnetostratigraphy was born.

Seafloor Stripes

Also remarkable was the prediction by Fred Vine and Drummond Matthews of Cambridge that because of ongoing seafloor spreading and the reversals of Earth’s magnetic field, the magnetism of the ocean floor rocks should be arranged as a series of stripes of normally and reversely magnetized crust. They proposed that these stripes run parallel to and symmetrical with the mid-ocean ridges [Vine and Matthews, 1963].

Studies of the magnetic pattern on the Reykjanes Ridge south of Iceland reported at the meeting showed exactly this configuration of reversed and normally magnetized crust. By towing a magnetometer (an instrument that records the strength of Earth’s magnetic field) behind a ship, researchers discovered that when a magnetometer passes over normally magnetized ocean floor, Earth’s magnetic field is enhanced, whereas over reversely magnetized ocean crust the magnetic field is weakened.

The pattern of normal and reversed stripes of ocean floor matched the pattern of geomagnetic reversals found by dating the rocks from continents and oceanic islands and also matched that discovered by Opdyke in his deep-sea cores.

Magic Magnetic Profiles

(top) Magnetic anomalies, imaged by while traveling across a mid-ocean ridge near Antarctica. (middle) A mirror image of the top profile, reflected across the ridge axis. Note the symmetry in the two profiles. (bottom) A model generated by assuming normal and reversed ocean crust as shown as black and white banded chrons. Credit: Pitman and Heirtzler, [1966]/AAAS
(Top) Magnetic anomalies, imaged while traveling across a mid-ocean ridge near Antarctica. (middle) A mirror image of the top profile, reflected across the ridge axis. Note the symmetry in the two profiles. (bottom) A model generated by assuming normal and reversed ocean crust as shown as black and white banded chrons. Credit: Pitman and Heirtzler [1966]/AAAS
Probably the most astounding discovery was the first report of the R/V Eltanin 19 “magic” magnetic profile, taken as the ship traveled across the Pacific Antarctic sector of the mid-ocean ridge. The discovery, presented by Walter Pitman and Jim Heirtzler from Lamont, showed the same symmetrical magnetic anomalies occurring in the ocean basins far from the axes of the ocean ridges, going back more than 10 million years in geologic time [Pitman and Heirtzler, 1966].

What’s more, Pitman and Heirtzler demonstrated that the patterns of magnetic anomalies could be reproduced by models in which the seafloor was spreading at rates from 1 to a few centimeters per year. They shared their findings at the symposium, and within a few years, scientists were able to use the same techniques to extend the magnetic timescale back more than 70 million years.

Confirmation from Around the World

The confluence of those three lines of research—tracing the Earth’s magnetic reversals in volcanic rocks, in cores of sediment, and on the oceanic crust—transformed geology and geophysics from a collection of unrelated data to a new and dynamic subject. These discoveries would ultimately contribute to a paradigm shift in the geosciences.

Edward Bullard of Cambridge University discusses heat flow at the History of the Earth’s Crust Symposium.
Edward Bullard of Cambridge University discusses the distribution of heat flow from the oceanic crust at the History of the Earth’s Crust Symposium. Credit: Barrett Gallagher

Independent evidence of seafloor spreading came from measurements of oceanic heat flow by Xavier Le Pichon, who showed excess heating over the ocean ridges, with the crust cooling and subsiding as one moved farther from the ridge crest [Langseth et al., 1966]. Seismological evidence developed by Lynn Sykes at Lamont showed that earthquakes were occurring along the axis of the mid-ocean ridge and on sectors of transverse offsetting faults between the ridge segments [Sykes, 1967]. Using first-motion studies of the earthquakes, Sykes showed that the movement along the faults was not in the direction of the offsets, as might be expected, but the reverse. They were not transcurrent faults but “transform faults” as hypothesized by Wilson [1965] just a year earlier.

Independent geologic evidence of continental drift was also presented at the symposium in the form of Edward Bullard’s computer fit of the continents around the Atlantic Ocean [Bullard et al., 1965], Pat Hurley’s compilation of ancient radiometric age data of the continents from West Africa and South America showing that the patterns matched [Hurley et al., 1967], John Dewey and Marshall Kay’s reconstruction of the Appalachians and Caledonides prior to the origin of the present Atlantic Ocean [Dewey and Kay, 1968], and the presentation of polar wander (now seen as mostly the result of continental drift) by Ted Irving of the University of Leeds [Irving, 1964] and others.

Edging Toward a Paradigm Shift

Scientists discuss seafloor spreading at the History of the Earth’s Crust Symposium.
Harry Hess of Princeton University (at left) discusses seafloor spreading with attendees at the History of the Earth’s Crust Symposium. Paul Gast of Columbia University is at right. Credit: Barrett Gallagher

After the meeting, a number of conference attendees returned to their respective institutions convinced that global tectonics provided the best explanation for the magnetic signatures they had observed.

This was but one piece of the puzzle. Over the next year, scientists took these paleomagnetic data and combined them with observations of the seafloor, with the mechanics of ridges, and with maps of global earthquakes and known volcanoes to create a unified theory of plate tectonics [McKenzie and Parker, 1967; Morgan, 1968].

The work presented at the meeting, and the work of many others, contributed to the resolution of a key revolution in geophysical thought. Now, as we give our talks and present our posters at the Fall Meeting, we can find inspiration in this gathering of scientists half a century ago. We are still feeling the repercussions of that disciplinary paradigm shift today.

What new fields of research might be born through presentations and scientific discussions this week in San Francisco? We’ll have to wait and see.

References

Bullard, E. C., J. E. Everett, and A. G. Smith (1965), Fit of continents around the Atlantic, Philos. Trans. R. Soc. London A, 258, 41–75.

Cox, A., R. R. Doell, and G. B. Dalrymple (1964), Reversals of the Earth’s magnetic field, Science, 144, 1537–1543.

Dewey, J., and M. Kay (1968), Appalachian and Caledonian evidence for drift in the North Atlantic, in The History of the Earth’s Crust: A Symposium, edited by R. A. Phinney, pp. 161–167, Princeton Univ. Press, Princeton, N.J.

Hurley, P. M., et al. (1967), Test of continental drift by comparison of radiometric ages, Science, 157, 495–500.

Irving, E. (1964), Paleomagnetism and Its Application to Geological and Geophysical Problems, John Wiley, New York.

Langseth, M. G., Jr., X. Le Pichon, and M. Ewing (1966), Crustal structure of the mid-ocean ridges: 5. Heat flow through the Atlantic Ocean floor and convection currents, J. Geophys. Res., 71(22), 5321–5355, doi:10.1029/JZ071i022p05321.

McKenzie, D. P., and D. L. Parker (1967), The North Pacific: An example of tectonics on a sphere, Nature, 216, 1276–1280, doi:10.1038/2161276a0.

Morgan, W. J. (1968), Rises, trenches, great faults, and crustal blocks, J. Geophys. Res., 73(6), 1959–1982, doi:10.1029/JB073i006p01959.

Opdyke, N. D., et al. (1966), Paleomagnetic study of Antarctic deep-sea cores, Science, 154, 349–357.

Oreskes, N. (1999), The Rejection of Continental Drift: Theory and Method in American Earth Science, 432 pp., Oxford Univ. Press, Oxford, U. K.

Phinney, R. A. (Ed.) (1968), The History of the Earth’s Crust: A Symposium, 244 pp., Princeton Univ. Press, Princeton, N.J.

Pitman, W. C., and J. P. Heirtzler (1966), Magnetic anomalies over the Pacific-Antarctic ridge, Science, 154, 1164–1171.

Sykes, L. R. (1967), Mechanisms of earthquakes and nature of faulting on the mid-ocean ridges, J. Geophys. Res., 72, 2131–2153, doi:10.1029/JZ072i008p02131.

Vine, F. J., and D. H. Matthews (1963), Magnetic anomalies over oceanic ridges, Nature, 199, 947–949.

Wilson, J. T. (1965), A new class of faults and their bearing on continental drift, Nature, 207, 343–347.

Author Information

Michael R. Rampino (email: [email protected]), Department of Biology and Department of Environmental Studies, New York University, New York

Correction, 29 December 2016: Title and text have been changed to better reflect historical context behind the History of the Earth’s Crust Symposium. The meeting was not in itself a catalyst for the paradigm shift toward the acceptance of the theory of global tectonics. Rather, it was a step along a lengthy road that preceded this shift. Eos thanks careful readers for pointing this out.

Citation: Rampino, M. R. (2016), A meeting that helped foster the acceptance of global tectonics, Eos, 97, https://doi.org/10.1029/2016EO063933. Published on 12 December 2016.
© 2016. The authors. CC BY 3.0
  • AGUEOS

    29 December 2016: Title and text have been changed to better reflect historical context behind the History of the Earth’s Crust Symposium. The meeting was not in itself a catalyst for the paradigm shift toward the acceptance of the theory of global tectonics. Rather, it was a step along a lengthy road that preceded this
    shift. Eos thanks careful readers for pointing this out.

  • Keith Tinkler

    However you want to phrase it, that continents moved and were responsible for the matching patterns of continental geology, was certainly being taught in a first year Geology class by Prof Robert Shackleton at Liverpool (UK) in the Fall of 1960. It was taken for granted, since Arthur Holmes’ textbook was used in the course (and was also used in the Advanced level Physical Geography courses in the Grammar schools, very few of which taught Advanced Geology.)

  • Hendrik

    Interesting article but by then it was already an established concept. So claiming
    that this was the meeting that gave birth to the idea is a bit rich.
    Alex Du Toit had published “Our Wandering continents” 30 years before
    this meeting. Come on guys, you gotta up your game a bit
    https://www.e-education.psu.edu/earth520/node/1796
    https://www.cambridge.org/…/2391EFEA9BFECAF67BA1EFF8C61…
    http://www.indiana.edu/~tecton/notes/lecture_2-1.pdf

  • Januka Attanayake

    A nice article summarizing the work that took place between 1960 and1970, during which time solid evidence of Plate Tectonics came to the fore. Of course there are several other names that deserve credit. This is a great source of information to introduce plate tectonics to intro-Geo classes!

  • rick4606

    Interesting, but incomplete. The real story starts 30 years earlier when Samuel Carey started promoting his subduction, spreading ridge and mobile plate tectonic theory. It is actually documented by Google books Ngram Viewer when setting the date span to 1930-2010 and entering ‘subduction” or alternatively “plate tectonics”. The first bump, interrupted by WWII and a post-war hiatus, runs from about 1937 to 1960 when Carey’s plate tectonic buzzwords entered Google’s vast corpus of literature. Carey tried unsuccessfully to gain establishment acceptance of his wild and crazy theory, The second bump begins in September 1968 when the “New Global Tectonics” went mainstream and was relabeled Plate Tectonics in 1969. It is interesting to read the literature and correspondence of the day to see some of the earth scientists mentioned above deciding, between 1964 and 1967, which of Carey’s theories, (“subduction tectonics” or “expansion tectonics”), should be adopted to explain the growing body of oceanographic information. I suspect that the NASA funding frenzy of the 1960’s doomed Carey’s expansion option since it required the earth’s mass to increase, thereby directly contradicting the trending inflation theory of the universe which got its own trendy name in 1965-1966 following the reported discovery of the long sought Cosmic Microwave Background. If anyone is interested I can send a screenshot of a Powerpoint slide showing the Google books Ngram Viewer result described above. My email is [email protected]

  • Laura Crossey

    Surely many attendees and presenters would have been aware of Bob Dietz’s 1961 Nature paper where he coined the term ‘sea floor spreading’! And as others have noted, a broad international recognition existed. This meeting was hardly the birth. Nonetheless, an important point where many on the fence probably recognized the science. Maybe a christening?!

  • Marilyn Browning Vogel

    Check out Naomi Oreskes’ “The Rejection of Continental Drift”, esp. Ch 9. Wegener/Taylor and Arthur Holmes correctly described both the evidence and mechanisms for moving plates decades before, and most non-American geoscientists accepted their (correct) paradigm. While many new observations had come to light by 1966…It was only a paradigm shift or a “new idea” for the American geoscientific community, which had worked hard for decades to discredit the Wegener/Holmes/Taylor theory of continental drift…

    • Mark Duffett

      Indeed, in the first photo above, at the base of the projected figure, can be interpolated the caption ‘Fit of Africa and South America (From Carey 19??). The Carey reference is probably to ‘Continental drift : a symposium : being a symposium on the present status of the continental drift hypothesis, held in the Geology Department of the University of Tasmania, in March, 1956’ / convenor, S. Warren Carey. This meeting, ten years earlier, would have at least as strong a claim as progenitor to the global acceptance of global tectonics.